1. Field of the Invention
The present invention relates to a biosensor for measuring gas, and more particularly to an enzymatic gas biosensor and the manufacturing method thereof, which can measure oxidization of a gas-phase organic chemical by enzymatic reaction, utilizing a thick film electrochemical device.
2. Description of the Prior Art
Conventionally, electrochemical measurement type biosensors have been made by immobilizing, as a membrane, enzymes or micro-organisms on the surface of an electrode such as an H.sub.2 O.sub.2 electrode, an oxygen electrode, an ammonium (NH.sub.4 +) ion-selective electrode, etc., or of an ISFET (ion-selective field effect transistor). Such type of biosensor can detect and measure an electrode-active material formed as the result of a single or multi-step enzymatic reaction. U.S. Pat. No. 4,655,880 discloses such a biosensor in which various kinds of oxidase materials are immobilized on a thick film electrochemical device to measure electrode-active materials.
Meanwhile, biosensors utilizing oxide-semiconductors are now widely used for measuring gas-phase chemicals, which measure the change of conductivity when reducing gas such as methane, carbon monoxide, etc. is oxidized on the surface of the sensor.
In the fields of a gas-solid bioreactor and the analysis thereof, conversion reaction of a gas-phase organic chemical by a dried enzyme has now been an important theme for study, and there has been great amounts of research for its application in the field of biotechnology. For example, a bioreactor in which alcohol dehydrogenase and NAD (.beta.-Nicotinamide adenine dinucleotide) or NADH (the reduced form of NAD) are treated with albumin and glutaraldehyde has been developed to form a gas-phase product by utilizing a gas-phase substrate (Biotechnol. Letters. 8(11): 783-784). Also, another bioreactor in which alcohol oxidase and catalase are adsorbed to DEAE-cellulose (diethyl aminoethyl-cellulose) or controlled pore glass (CPG) has been developed for a similar purpose (Biotechnol. Bioeng. 34:1178-1185).
Sensors and methods for measuring gas-phase organic chemicals utilizing enzymes are known in the art. U.S. Pat. No. 4,525,704 discloses an enzymatic toxic gas sensor utilizing the fact that the activity of enzymatic reaction is inhibited due to the existence of a toxic material such as an organic phosphoric pesticide. International Application No. 88/01299 teaches a method of measuring the change of color using a color-forming reagent after immobilizing an enzyme on an organic or inorganic carrier.
An alcohol checker generally adopts a gas sensor, for example, TGS822 gas sensor manufactured by Figaro Co., Ltd., Japan, and thus can measure the concentration of alcohol which is contained in gases generated in human breathing.
Meanwhile, Japanese Patent Publication Nos. Sho 60-196198 and Sho 60-172298 teach measuring methods utilizing enzymatic reaction, whereby alcohol contained in an aqueous solution (or in the human's saliva) is measured using a strip-shaped test paper. According to the method disclosed in International Application No. 88/01299, the concentration of alcohol contained in the gases generated in the human breathing is measured by utilizing the change of color.
However, conventional electrochemical measurement type biosensors have the drawback that they must be used in favorable conditions for bioreaction, i.e., in liquid. Accordingly, in order to measure a gas-phase specimen by means of the biosensor of electrochemical measurement type, a responsive membrane of the biosensor should serve as an immobilizing carrier with moisture properly retained as well as serve as an electrode system. Further, when the biosensor is used to react with a gas-phase specimen, electron transmission between the enzyme-responsive membrane and the electrode should be effected satisfactorily, and thus this requires a high-level electrode manufacturing technique and a high-level enzyme immobilizing technique as well.
The conventional gas biosensor utilizing the oxide-semiconductor also has the disadvantages that if it utilizes alcohol-responsive metal-oxide such as TiO.sub.2 and RuO.sub.2, it is difficult to quantitate alcohol since its selectivity with respect to alcohol deteriorates.
Meanwhile, a conventional biosensor for measuring a gas-phase organic chemical by utilizing enzymatic reaction can quantitate the chemical accurately because of the substrate specificity of the enzyme itself. However, according to the conventional method of measuring the change of color by utilizing 2,6-dichloroindophenol and so on (International Application No. 88/01299), it is also required to measure the absorbance in order to quantitate the organic chemical, resulting in inconvenient use.